Dinosaurs were land-dwelling reptiles that walked with an erect stance. Their unique hip structure caused their legs to stick out under their bodies, and not sprawl out from the side (as with other reptiles).

When dinosaurs first evolved from more primitive archosaurs, they were bipedal (they walked on two legs). Much later, some dinosaur groups returned to a four-legged stance, most having rear legs much larger than their front legs .

There were many different types of dinosaurs, differing in size and weight, locomotion (two- or four- legged walk, fast or slow speed), diet (meat or plants), and just about every other physiological and anatomical measure.
The following are just two of the many different types of dinosaurs.

The following drawing is of a typical large Sauropod, a four-legged, slow moving herbivore (eats plants):

The following drawing is of a typical theropod, a fast, two-legged carnivore (eats animals):